[Cob] seismic stability & related permits for cob structures

[otherfish]

To Charmaine & all,

In response to Charmaine's recent message, here is a piece I wrote some time
ago about dealing with seismic issues and building permits for cob
structures.
Hope this is helpful.
john fordice
.................
In June if 1998, I worked with Katie Jeane to help her get a building permit
for her cob house near Willits, California.  This is in Mendocino County,
which has the good fortune of being one of the three counties in California
which allow ³Class K² (owner builder) Building Permits.  Under this type of
permit, the owner-builder is exempted from many of the normal UBC permit
requirements. The County, due to a lack of understanding of cob, required
Katie to have an Architect of Engineer sign her plans, and this is how  I
became involved.  The task as I saw it was how to fulfill my legal and moral
obligations as a California Licensed Architect (i.e. make sure the building
design was structurally sound) and at the same time not subject Katie to the
cost of hiring a Structural Engineer.  On searching around, I found the
Getty Report  which lays out a set of simple Seismic Stability techniques
for use on historic adobe buildings.  As this was the closest thing going to
a tested and proven method of assuring that an earthen building will in fact
withstand a severe earthquake, I elected to employ  these techniques in the
plans for Katie¹s building.
Katie was thus able to get a permit for her building ( the first cob
specific building permit in California, to my knowledge), and the last I
heard, her building was nearing completion in the fall of 1999.

In 1995 The Getty Conservation Institute issued the report: ³Seismic
stabilization of historic adobe buildings².  In a nutshell, the report gives
us the following knowledge about adobe walls:

adobe walls will crack in a severe earthquake;
the wall height-to-thickness ratio effects wall performance;
a ratio of<4 will remain standing even if cracked by an earthquake;
a ratio of 4-6 (typical of historic adobe buildings) will usually remain
standing if cracked;
a ratio of 6-9 lessens in stability as the ratio increases and is likely to
collapse in strong earthquakes;
a ratio of 9-12 is likely to be unstable and collapse;
a ratio of>12 is unstable;
walls supporting a load from above are more stable than those not supporting
a load.

The stability methods tested in the Getty report and their earthquake
severity performance results are (in a range of 1  to 7 as  moderate to
severe): 
a stiff bond beam is effective if it has a positive connection to the wall
top (1-4);
a flexible bond beam performs better than a stiff bond beam (2-5);
horizontal straps along the walls act effectively to restrain the wall once
it cracks (3-6);
a flexible bond beam with vertical ties performs best (1-7).

Of the model structures which were shake table tested, the best performing
stability methods were a roof diphragm combined with either a flexible bond
beam with center wall ties, or a flexible bond beam with vertical and
horizontal straps on the outside of the walls.  These methods show a
survival potential of almost 3 times that required by the UBC.  This is
promising indeed.

In August of 1998 I began the construction of a cob toolshed at the
Northside Community Garden in Berkeley, California.  This a also small (<120
s.f.) building in an urban setting and we have not sought a building permit
on that basis.  Roughly triangular in plan, it employs a concrete bond beam
designed to grip the top of the wall,  1/4² dia. vertical wall ties @
roughly 24² o.c., and a mortared urbanite base wall on a reinforced concrete
footing.  The cob was mixed with the combination of a small cement mixer for
the earth, sand & water,  and foot stomping the straw on tarps.  The cob
walls and bond beams are completed to date and roof framing is just
starting.  The project has been done by all volunteer labor of a Saturday
morning basis.  We expect completion of the living roof by fall.

I am in the beginning phases of planning a cob studio for my backyard in
Berkeley.  There will be no avoiding a building permit on this one.  I have
had preliminary discussion with the Berkeley Building Department and it
appears will need to pursue the permit via the UBC Section on Alternate
Materials and Methods.   I had hoped to be able to invoke the techniques
from the Getty  testing, but at this point it seems doubtful that this will
happen.   Structural calculations will probably be required.  I have
contacted Fred Webster, a structural engineer with considerable knowledge in
earth buildings, and to do calculations he will require: architectural and
structural drawings;  the material properties of the cob (compressive
strength, modulus of rupture, clay content, and method of stabilization);
and  location of the project relative to known earthquake faults.  The
estimated cost for his services will be around $1250.  I¹m guessing that the
engineering requirements will not be the end of the Building Department¹s
concerns, and that an education process will need to take place.

Getting thru the Building Department in the absence of a coherent cob code
is going to be like reinventing the wheel.  Early strawbale buildings had
this problem, but now that there is a strawbale code available, there is
alot of strawbale building going on.  There is no reason that the same thing
cannot exist for cob.  It only takes the will for us to make it happen.

Remember, the Building Code is just a tool, designed & created by people to
do a specific job.  We as Natural Builders can take control of the code
situation if we so desire.  It¹s up to us.

Cob on !!!
john fordice 
.......................

on 12/28/03 3:15 PM, Charmaine Taylor at tms at northcoast.com wrote:

> Hello All, I am sure most are aware of the devastating quake in Bam, Iran
> which destroyed a 2000+ mud brick citadel..I went out looking for images, and
> found this from a personal  photo diary online...the images onTV were so
> beautiful it is sad to see it gone now.  But for those in earthquake zones (
> like CA)  I am now more aware of why reinforcement to cob walls  may also  be
> needed.  John Fordice, can you address this in some way for us as to how to
> strengthen cob walls, with or without metal rebar, etc?
> Ms. Charmaine  Taylor/ Taylor Publishing
> http://www.dirtcheapbuilder.com    http://www.papercrete.com
> PO Box 375, Cutten CA 95534
> 707-441-1632
> 
> 
> http://www.monkeyview.net/id/601/default/index.vhtml
> 
> http://www.monkeyview.net/id/601/default/index.vhtml
> 
> Bam Citadel, anywhere from 2000 to 3000 years old, is surprisingly
> intact. You can walk along the thick walls of the
> once-thriving city, climb
> the watchtower, spy the bazaar and stables structures below,
> as well as
> many dwellings. in fact, many dwellings were in use until
> people were
> removed by govnt mandate.
> Two things I found very impressive about ancient
> architecture of Iran:
> 1) buildings were often built in four parts, and use of the
> parts were
> rotated according to season. the winter section was smaller
> and more
> tightly sealed, easier to heat. the hot weather sections
> were strategically
> placed to avoid the worst of the sun during the active hours
> of the day.
> 2)they used windcatchers-cleverly placed holes in the upper
> walls and
> ceiling that would seize the breeze and optimize the
> circulation of cooler
> air.
> 3)ok, three things. the longevity of the buildings.
> 
> 
> http://www.monkeyview.net/id/601/default/index.vhtml
> at the top of the lookout post.
> http://www.monkeyview.net/id/601/default/index.vhtml
> 
>